The proposed work consists of a series of projects which employ measurements of the production and absorption of gases in the intestinal tract to study the physiology of the gut. These projects include: 1) Study of the metabolism of the colonic flora by analyzing the trace gases which are then excreted on the breath; 2) Study of intestinal blood flow by carbon monoxide absorption and blood flow determinations obtained with microspheres; 3) Study of intestinal malabsorption through measurement of breath H2 excretion and 14CO2 excretion. BIBLIOGRAPHIC REFERENCES: Bond, J.H. & Levitt, M.D. Fate of soluble carbohydrate in the colon of rats and man. J. Clin. Investigation 57:1158-1164, 1976. MicFlikier, A.B., Bond, J.H., Sircar, B., and Levitt, M.D. Intestinal villus blood flow measured with carbon monoxide and microspheres. Am. J. Physiology 230:916, 1976.